Many different kinds of fixing devices are known for mounting photovoltaic modules (PV modules) on sloping roofs, generally in a vertical orientation from the crown to the eaves, which fixing devices are all based on a common basic idea. In this case, the normal sloping roof consists of rafters which are arranged in a spacing of from 60 to 120 cm and define the roof slope. A sarking membrane is usually fixed to counter lathing and the roof laths on these rafters to keep out water and snow driven in by the wind. The individual elements of the roof covering are laid on the roof laths. All known roof covering materials which consist of uniform individual elements, e.g. corrugated sheets made from fiber cement, metal or wood clapboards and natural and artificial roofing tiles of all shapes, come into consideration for this purpose. The term roofing tile is used as a generalization in the following description for all roof claddings made from individual elements.
Roof hooks made from bent sheet steel or aluminum profile are preferably screwed to the rafters and passed through between the roofing tiles as fixing devices to fix PV modules. In order to enable the passing through of the roof hooks, either the roofing tiles must be reworked in terms of the width and thickness of the roofing hook, e.g. by processing with a hand grinder, or the roofing tiles must be laid without reworking, accepting a gap in the covering region. As a result of the reworking, any guarantee for the sealing of the roof covering is voided. Additionally, the roofing tiles can be destroyed or weakened to such a degree in the process that they must be replaced in the further course of the work or, in the worst case, will have a markedly shortened lifetime. Falling roofing tile pieces represent a significant danger. In addition to people, the PV modules can also be damaged. In the event that reworking is not carried out, the look and also the sealing of the roof covering is adversely affected.
A rail system, on which the PV modules can later be arranged, can be fixed onto or to the roof hook in the manner specified by the manufacturer. Disadvantageous in the case of these systems is the fact that snow and wind loads acting on the PV module act perpendicularly to the roof surface and press the roof hook in the direction of the roofing tile. If insufficient spacing of the roof hook from the roofing tile is present, the latter can be destroyed under the load.
A fixing device for solar collectors and/or PV modules, which, depending on the embodiment, has rigid roof hooks for hanging over roof laths or screwing to roof rafters, is described in DE 20 2004 008 499 U1. The rigid roof hooks are either formed from two brackets, whereby their connecting point is a screw connection with an elongated hole for setting the thickness of the roof laths, or formed from three brackets, whereby, in turn, a connecting point is used for setting the thickness of the roof lath and the second connecting point allows the length of the arm, which should accommodate the PV module, to be set, likewise with the aid of a screw connection with an elongated hole. For static reasons, the brackets have a relatively large rectangular metal section which must penetrate through the roof covering, that is to say between two roofing tiles which are arranged in such a manner as to be mutually overlapping, over its entire width. In addition, it is necessary, for aesthetic reasons and for the sealing of the roof covering, to process the roofing tile located under the rigid roof hook in terms of the width and thickness of the roof hook material, in order to obtain a corresponding accommodating groove. The processing of the roofing tile is expensive, time consuming and is associated with the voiding of the guarantee for the roofing tile and therefore the sealing of the roof covering. Furthermore, the rigid roof hook can, in the event of snow or wind loads arising, break the roofing tile located beneath it, due to the weakening brought about by its accommodating groove in which it lies, and therefore likewise destroy the sealing of the roof covering and endanger people by falling.
A fixing device for mounting PV modules on roofs, which device has a rigid roof hook which is formed in one piece and produced from cast aluminum in its basic form, is described in DE 10 2005 043 957 B3. The shape of the rigid roof hook only allows it to be fixed practically to roof rafters. Its one-piece construction without setting possibilities makes it in every dimensional value disadvantageously usable only for one design of a roof with particular roof laths, counter laths (in some cases) and roofing tiles. In this case also, the profile of the rigid roof hook is relatively large and rectangular for static reasons. It must also penetrate through the roof covering between two roofing tiles which are arranged in such a manner as to be mutually overlapping. The processing of the roofing tile necessary for this purpose is associated with the previously indicated disadvantages.
A fixing device for mounting PV modules on roofs, which device again has a roof hook which can be fixed to roof rafters and does not have a setting element, so that it is in each case only suitable for one roof design, is described in DE 10 2004 057 041 A1. The roof hook is configured in the shape of a spiral spring and allows mounting of the solar module above the roof covering without touching the latter. In the event of wind load, the spring action of the load on the roofing tile surrounded by the roof hook can thus be reduced. However, in this case also, the hook profile is relatively large and rectangular for static reasons. It must also penetrate through the roof covering between two roofing tiles and the processing necessary for this purpose is associated with the already known disadvantages.
A further fixing device with relatively large roof hooks is described in DE 103 44 202 A1. As an alternative, fixing devices with special roofing tiles with inset rail systems are shown. The fixing device with roof hooks does not differ substantially from the fixing devices with the known disadvantages described further above. The fixing device with special roofing tiles is limited to the roofing tile formats produced with it and cannot therefore be used everywhere.
A fixing device for mounting PV modules on roofs with sheet metal cladding is described in DE 10 2005 061 709 A1. Here, the relatively large roof hooks are fixed externally to the roof covering, whereby rivets penetrating the roof covering are used.
In the Brochure I, “The ClickFit Mounting Structure for PV Systems” from the company ClickFit (which can be accessed at the Internet address click-fit.com/download/ClickFit-Brochure-EN.pdf, as of Jan. 9, 2008), the system and the use of simple roof hooks for fixing rails is described in clear images and associated texts. The rails then accommodate the photovoltaic modules. It becomes clear that in the case of unprocessed roofing tiles, the next roof layer cannot rest flushly over the roof hook.
In the Brochure II “LORENZ SoloSolar module mounting system, Pitched roof, one layer” from the company energiebau solarstromsysteme gmbh (which can be accessed at the Internet address eb.etamis.de/05_downloads/03_montage/01_LORENZ_solo.pdf as of Jan. 9, 2008), a further roof hook system is described in the graphics, which roof hook system clearly shows a processed roofing tile (plain tile) in the middle image on page 3.